1. Field of the Invention
The present invention relates to a high-frequency signal transmission line and an electronic device, and more specifically relates to a high-frequency signal transmission line and an electronic device, in each of which a signal line is provided in a body including laminated insulator layers.
2. Description of the Related Art
As a high-frequency signal transmission line of the related art, a microstrip flexible substrate connection line has been known that is described in, for example, Japanese Unexamined Patent Application Publication No. 9-139610. In the microstrip flexible substrate connection line, microstrip lines are formed with sandwiching therebetween a thin flexible dielectric substrate. Such a microstrip flexible substrate connection line is thinner than a coaxial cable. Therefore, it is easy to dispose the microstrip flexible substrate connection line in a narrow space within a wireless communication terminal.
Incidentally, in a case where circuit substrates are connected to each other using the microstrip flexible substrate connection line described in Japanese Unexamined Patent Application Publication No. 9-139610, it may be considered that a coaxial connector receptacle described in, for example, Japanese Patent No. 3161281 is used. Specifically, the coaxial connector receptacle is mounted on one end of the microstrip flexible substrate connection line. In addition, the coaxial connector receptacle is attached to a coaxial connector plug provided in a circuit substrate, and hence, the microstrip flexible substrate connection line is connected to the circuit substrate. As a result, it becomes possible to easily connect the microstrip flexible substrate connection line to the circuit substrate.
However, in a case where the coaxial connector receptacle is applied to the microstrip flexible substrate connection line, there is a possibility that the characteristic impedance of a signal line is mismatched with respect to a predetermined characteristic impedance (for example, 50Ω). In more detail, the coaxial connector receptacle is configured by a plurality of parts. Therefore, stray capacitance or parasitic inductance easily occurs in the coaxial connector receptacle, and the characteristic impedance of the coaxial connector receptacle is easily mismatched with respect to the predetermined characteristic impedance. Furthermore, there is a possibility that coaxial connector receptacles having various structures are mounted on the microstrip flexible substrate connection line. Therefore, there is a possibility that a characteristic impedance varies with respect to each type of coaxial connector receptacle. As described above, if the characteristic impedance of the coaxial connector receptacle is mismatched with respect to the predetermined characteristic impedance, the reflection of a high-frequency signal occurs in the coaxial connector receptacle.
In addition, even in a case where the coaxial connector receptacle is not used, there is a possibility that the characteristic impedance of the signal line is mismatched with respect to the predetermined characteristic impedance, due to the following reason. In a case where the coaxial connector receptacle is not used, an external electrode, connected to the signal line, is provided on the surface of an end portion of the microstrip flexible substrate connection line. In addition, in a case where the microstrip flexible substrate connection line is connected to a circuit substrate, the external electrode is connected to a land electrode in the circuit substrate by a solder or the like. In this case, in the vicinity of the external electrode, a conductor shape or the like is different compared with the forming region of the signal line, and the characteristic impedance of an external electrode portion is different from the forming region of the signal line in some cases. As a result, there is a possibility that the characteristic impedance of the signal line is mismatched with respect to the predetermined characteristic impedance.